Niles Eldredge - The Darwin Blogs

The Darwin Blogs – October 11, 2006.

Mr. Darwin Writes Again—and Issues a Challenge, to Which I Reply

I am happy to say that, after a brief hiatus, Charles Darwin has once again contacted me—again in the form of an email, the digital version of his penchant—when alive—to write letters constantly, asking for data and exchanging ideas in geology, paleontology, botany, and zoology with an amazing range of people.

October 10, 2006

My Dear Eldredge

Pardon my brief absence. As you surmised, I was awaiting your promised completion of your thoughts on why America, nearly uniquely, has seen so much controversy surrounding my views in its legislative and especially judicial systems. It is interesting indeed to have learned that an innovation concerning the protection of the rights to practice any religion freely, ensconced in your Founding legal document, has become the de facto source of legal redress to attempts to install the various Poppycock versions of Creationism in the curricula of your schools. Bravo!

I also feel a bit chastened when you point out that it is not, in fact, only "my views" which are so fiercely opposed. You are of course quite right in pointing out that evolutionary biology has made great strides since my death—so it is modern evolutionary thought that is opposed by creationists. Still, I must say that the debate seems to have changed but little from my day—the creationists and "evolutionists" alike are saying substantially the same things to one another as were said even before I was born! And I will remind you of your earlier observation in these Blogs of yours (though named for me!) that "Darwinism" is a synonym of "evolution."

I have not been wholly idle in the interim, however. As you are aware, beginning soon after my return in the Fall of 1836, I began exploring in my Transmutation Notebook B the themes of variation and inheritance—the better to identify a means whereby new species might be seen to originate through natural law. Indeed, I labeled my discussion "Zoonomia" after my grandfather's (i.e. Erasmus Darwin) work of that title. In invokingv his spirit (as it were) I was by no means content to settle for his often somewhat fanciful speculations. Rather, I was intent on summarizing what was known at the time of these matters—and to explore very carefully and logically the connections such processes might have to the search for an explanation of how animal and plant species might change over time. These interests stayed with me for the rest of my life—especially in my various experiments and observations made over the years in the fields, gardens and greenhouse at my house in Downe.

As I believe you yourself have remarked—and with all due respect for your own Field of Paleontology—it is in precisely these areas of inheritance and variation that most of the progress in Knowledge has been made in the years since my death in 1882. I am eternally (!) grateful to the Internet, which has proven already in these past few weeks since I have arrived here and have encountered the Digital Ether, to be most highly informative on these matters. Paleontology (I do hope I do not offend you with this remark) by contrast seems not to have made nearly so much significant progress in its understanding since my day—beyond of course the much more detailed knowledge of the actual history of life (especially, I gather, of Precambrian simple life forms previously wholly unknown to us—as well as a splendid array of human fossils). You may disagree.

Still, I am a neophyte with much catching-up to do—however keen, nay passionate, my appetite is for learning all that there is to be learnt concerning these issues of inheritance and variation. I have learnt that Mr. Weismann was making important strides even as my own life was drawing to a close—especially in his dictum that the germ cells (sperm and eggs of animals, e.g.) determine the properties of all the rest of the body cells (aptly termed the "soma")—but that the reverse is not true. What happens to a plant or animal in its lifetime does NOT affect its germ-line cells—and hence cannot be passed along to succeeding generations.

What a black eye for the theories of Lamarck! And I now regret more than ever that, in the sixth edition of my Origin of Species (the edition that appeared in 1872—and the one that I gather from Internet sources is the most widely available today) I bowed to pressure and admitted the possibility of the inheritance of "acquired
characteristics" in the manner alluded to by M. Lamarck.

I have learnt as well of the experimental results of the Austrian Monk, Gregor Mendel—and how his observations of green peas led to elucidation of some simple rules of inheritance based on the assumption of the particulate nature of the hereditary material. These were later called "genes," (and their study "genetics") when Mendel's work was apparently rediscovered by no fewer than three separate parties at the turn of the previous century (when I had been already gone for nearly twenty years).

But then to have to cope with the so-called "Molecular Revolution" on top of all this! My head fairly reels—with delight and admiration every bit as much as with the sheer dismay of having to absorb the myriad details that seem to still emerge each passing day!

But enough of my remedial schooling, which I shall continue as time permits. Though I was (as I remarked above) delighted to hear your more complete thoughts on the legal issues surrounding creationism in your country, it was your second news item of the October 8 "Blog," that truly caught my eye. That—and your accompanying, and I dare say maddeningly elliptic comment accusing me of having ignored evidence that you say pointed to what you have called "punctuated equilibria" and "turnovers."

You seemed (perhaps unsuitably overly) elated over the announcement in the journal Science (which publication was already in existence in my lifetime—if I am correct in assuming it is one and the same) of supposed confirmation of your views derived from the study of paleontology by scientists in my native country who analyzed evolutionary trees based on molecular evidence—and found that fully 22% of the changes in the "DNA" recorded in these trees occurred in so-called "punctuational" events.

My understanding of such matters is still so lamentably rudimentary that I will—at least for the moment—pass over the molecular study itself. I shall instead address what I gather is your own work (and that of colleagues such as Stephen Jay Gould and Elisabeth S. Vrba, whom you cite) in the Field of Paleontology.

I have many things to say—far too many to discuss in detail in what is already growing into an overly long letter. Suffice it to say, my dear Eldredge, that I was already fully aware of this matter of stasis, the long periods of their history in which species appear not to have changed much at all. I was aware as well of the importance of isolation in the formation of new species. I believe your insistence that my views—especially as articulated in my mature works, particularly On the Origin of Species—that I saw the origin of new species as simply the outcome of long periods of gradual change, to be a vast oversimplification of my true views on the matter. And as to these so-called "turnovers," I cannot remember having discussed them at all—having thought them to be the outmoded and discredited figments of M. Georges Cuvier's imagination.

Perhaps you might comment on some—or all—of these four points. I am especially vexed by your charge that I ignored evidence at my disposal that might have led to my consideration of these issues more nearly along the lines in which you have subsequently developed them.

Now it is my turn to await your reply.

My dear Sir, I remain your faithful correspondent.

C. Darwin

Wonderful! I have been longing for a chance to have this dialogue with Darwin for most of my professional life—the more so since I have read his early notebooks and unpublished manuscripts in recent years, and have seen first-hand how his thinking "evolved" over the years. Here's my reply:

October 11, 2006

Dear Charles (if I may—we Americans are an informal bunch!)

Thank you so much for getting back in touch!

I am not surprised in the least that you have been so immersed in the science of genetics—and of course [and despite your backhand slap at the conceptual growth in paleontology (or the lack thereof) over the same interval], I agree that for sheer revolution in knowledge, the prodigious changes in the science of heredity would of course occupy most of your catch-up time.

I had always thought, for example, that were you able to enter our exhibition on your life and work in the normal manner of a corporeal human being, you would have made a bee-line straight to the back of the hall to gobble up as much as possible about modern evolutionary science—going back only after having had your fill of new discoveries and conceptual advances since your death, to find your old family and friends in the form of paintings, photos, letters, manuscripts—as well as some of your very own material possessions that accompanied you during various stages of your life.

But I am surprised that you did not make the important point that your idea of evolution through natural selection remains very much intact, very much at the heart of modern thinking about the evolutionary process, despite the fact that your understanding of how organisms come to resemble their parents (the basic notion of heredity) and WHY there is heritable variation in populations was rudimentary at best—and downright erroneous at worst. (Your theory of Pangenesis was utterly wrong—though I have heard that in some letters, and indeed in some passages in some of your later works, you actually came close to spelling out some of Mendel's conclusions—as usual, nothing much truly eluded you!).

So perhaps, despite the enormous sea-change in our understanding of such matters as the years have gone by, there has resulted in something less than a conceptual revolution in our understanding of evolution as I take you to imply has occurred. As the great evolutionary geneticist Theodosius Dobzhansky (whose works are not yet posted on Internet sources—so you cannot have encountered them) pointed out so clearly in 1937, natural selection (and another process, "genetic drift") take place within populations of organisms—while inheritance and the origin of variation occur at the level of individual organisms. Thus all that is needed for natural selection to take place is that inheritance and variation occur (along with the Malthusian point of overproduction of young!—and even that is debated sometimes)—regardless, that is, of HOW variation and inheritance occur. You were right back then—and you remain right today!

You are unhappy, Charles, that I said (admittedly without substantiating evidence) that you had ignored certain lines of evidence that pointed to stasis and turnovers—those events where many species become extinct within a relatively short period of time—and new species appear (through evolution as well as migration—in essence to take the place of the newly extinct species).

And you take me up on four specific points—saying that (1) you were aware of stasis and of (2) the importance of isolation in evolution; you further state (3) that the suggestion that you believed in a strict form of gradual evolution is an egregious over-simplification; and, finally, (4) that you don't recall even having mentioned "turnovers"—thereby implying, I assume, that you didn't take them to be empirically "real" phenomena.

Charles, I have discussed these issues extensively—most recently in my book Darwin. Discovering the Tree of Life W.W. Norton, 2005). But of course these sources are not available to you—and besides, you of all people deserve a direct answer.

I shall try to provide a direct answer in the briefest terms—as, like you, I dislike overly long letters: they tend to take on the semblance of a polemic.

So let me just say, with regard to stasis, that you indeed had remarked on it. Especially in your Transmutation Notebooks of the late 1830s where in several passages you talk of the controversy (emanating from the Natural History Museum in France) over the mummified remains of species such as the Sacred Ibis that had been excavated from tombs during the Napoleonic invasion of Egypt. These mummies revealed that the species have remained essentially unchanged since those ancient times. Creationists saw these mummies as evidence of the stability of species—as an argument against "transmutation." Evolutionists—such as yourself—on the other hand tended to think there had been too little time gone by to expect much, if any, evolutionary change (for example, in Notebook E, pp. 4-5, you state that "It cannot be objected to my theory that the amount of change within historical times has been small—because change in forms is solely adaptation of whole of one race to some change in circumstances; now we know how slowly and insensibly such changes are in progress.")

I need hardly point out that, in making this point re lack of evolutionary change within historical times, you have written a passage (albeit unpublished in your lifetime—but similar passages appear in the Origin) proclaiming evolution to be primarily a matter of the slow steady transformation of entire species in response to environmental change—leaving an expected pattern of "insensibly graded series" in the fossil record!

At one spot—near the very beginning of your first Transmutation Notebook (i.e. Notebook B)—you wrote (pp. 6-8) "Aegyptian cats & dogs ibis same as formerly, but

separate a pair and place them on fresh island, it is very doubtful whether they remain constant…" You are claiming here that isolation inevitably leads to evolutionary differentiation—that the lack of change between mummies and modern examples of ibises etc. reflects a lack of such environmental change. And this passage (and many more) of course does support your contention that you felt isolation to be a key ingredient of the evolutionary process.

But consider this: in the Origin (p. 105 of the First edition) you state that "Although I do not doubt that isolation is of considerable importance in the production of new species, on the whole I am inclined to believe that largeness of area is of more importance, more especially in the production of species, which will prove capable of enduring for a long period, and of spreading widely." The historian Frank Sulloway, in an important paper published in 1979, documents your retreat from your earlier conclusions that isolation is VERY important in evolution (a view I have no doubt was brought on by your experience in the Galapagos Islands—as well as on islands elsewhere along the coast of South America). I have concluded that the position you take in the passage just quoted reflects your desire to develop the most general form of evolutionary theory possible—and there are simply more species living on continents than on archipelagos. The problem for you then became: How does isolation occur on continents? Not knowing then what we now know concerning the effects of climate change on continents, it was difficult for you to imagine how isolation could occur on continents (though you remark in some of your Beagle notes, and again in the first edition of your Journal of Researches (1839—aka The Voyage of the Beagle, first edition)that you could see mountain ranges providing such isolating effects.

Sulloway (1979) recounts the history of your correspondence with the German zoologist Moritz Wagner after the Origin had been published. Wagner was obsessed with the importance of isolation in evolution—and according to Sulloway (my German is poor—and I have not read the original correspondence) castigated you for not emphasizing more the role of isolation in evolution. Amazingly, Wagner's own theory appears to have been very like our own "punctuated equilibria": Wagner felt that small isolated populations could evolve very rapidly; when a new species emerged after a short period of time in isolation, and if it was successful, it would tend to spread—and evolution would slow to a crawl. There it is: rapid evolution in isolation followed by stasis! And this from a man with apparently little or no familiarity with the fossil record! (In this regard, it is fascinating to quote the following sentence from the paper by Pagel et al. published this past week, and discussed so extensively in the previous blog: "If speciation is associated with small founder populations and if genetic isolation is maintained, evolutionary rates can be accelerated at potentially all loci….").

Now, my work with historian David Kohn on the subject of your "Principle of Divergence" is not yet finished: but suffice it to say that the version left unpublished in your lifetime is far more complete than the version briefly sketched in the Origin—and the more complete version indeed supports your claim that simple linear phyletic gradualism was only one of a range of possible models (modern term for subset of theoretical ideas) of how new species can arise over large tracts of continental area—essentially without the imposition of absolute isolation. So I do agree that the image of you devoted strictly to "phyletic gradualism" is a bit cartoonish, and an oversimplification of your ideas. But I also maintain that it is not an entirely unfounded impression in the minds of those who have come after you.

One further word on stasis: you almost had the whole thing figured out! For near the end of Notebook E—well after you had the concept of natural selection well in hand, you wrote (pp. 135-136): "If separation in horizontal direction is far more important in making species, than time (as cause of change) which can hardly be believed, then, uniformity in geological formation intelligible." Therein, too, lie the kernels of "punctuated equilibria." But you didn't follow these ideas out.

Why not? Charles, I believe it was because, having finally nailed down the concept of natural selection, you then (and quite naturally) decided to rederive the patterns that brought you to accept transmutation in the first place: your experiences with fossil mammals in South America; replacement of one closely allied species by another over the terrain down there; and your observations on the Galapagos Islands and other islands elsewhere. Stasis and abrupt replacement in the fossil record seemed to you especially discordant with how you imagined natural selection to work. And so—and rather, I must say, unusually for you—you abandoned the facts of the matter (explaining them away in terms of inherent deficiencies in the fossil record) in favor of a theoretical construct.

Could it be that you came to realize this when—in your Autobiography written quite late in life—you said that for years you had thought that natural selection was your greatest contribution—but you had by then concluded that it was the convincing of the thinking world that transmutation—evolution—had occurred that was your real triumph? In reality, of course, BOTH aspects are essential to understanding why you are the Founding Father of all of us who labored in these disparate vineyards after you.

Summing up so far: as far as stasis, isolation and gradualism are concerned—what we see is that your youthful thoughts were more along the lines of the sorts of ideas expressed in "punctuated equilibria" than your definitive, later, PUBLISHED, thoughts.

This leaves only the matter of "turnovers" before I close this letter. Charles, you might be aware of, but in any case cannot have seen, a wonderful book entitled Foundations of the Origin of Species, published by your son Francis in 1909, in simultaneous celebration of your 100th birthday and the 50th anniversary of the publication of the Origin. In it, among many other previously unpublished treasures, Francis gives us a transcription of your 1842 Pencil Sketch (hands down my favorite essay of yours) and the much longer (and dare I say drier and less exciting) Essay of 1844—the manuscript you asked Emma to publish on the event of your death—and the manuscript that ended up dictating the eventual structure of the Origin.

Francis, in a footnote in tiny print (overlooked, as far as I can tell, by all subsequent historians) tells his readers that you had written a note in the "Fair Copy" of this manuscript, in the early pages devoted to the geological record: He reports that you wrote: "Better begin with this. If species really, after catastrophes, created in showers over world, my theory false."

So you see, my dear Charles, that at least in one place, you did confront the specter of turnovers! That you never actually did "begin with this" can only mean, in my opinion, that you were supremely uncomfortable with the possibility (after all, you wrote "my theory false!!). You found the possibility inconvenient, and simply wished it away—or so it seems to me.

More's the pity—as it has taken well over 100 years to re-establish the validity of Cuvier's original point of sudden demises of faunas—thanks to you and your arguments that convinced geologists and paleontologists that the patterns of stasis and turnovers in the fossil record reflect the vagaries of fossilization, the apparent patterns thereby being rendered as artifacts. I blame my colleagues—and the zoological and botanical communities as well—for being only too quick to follow your lead on this.

On the other hand, your insistence that the fact that gradualism is not more evident in the fossil record means that stasis is a chimera and turnovers not real events—has at the very least given me and an increasing number of colleagues, something to do with our careers! Something to be said for that!

For though these patterns now turn out to be real, your theory is NOT false! Just the particular version of your theory you derived as you imagined what the history of life should look like under the workings of natural selection. It was that specific image—and NOT the idea of evolution through natural selection—that was in large measure (if not completely) erroneous!

Charles, you were the early bird who got all the worms; that you had to pick and choose among them to craft a picture of evolution that you felt best fit the majority of cases—in all those mountains of data you accumulated during your lifetime—is understandable.

That we see things a bit differently now than then is in its own way "evolution." (and NOT gradual evolution, mind you!). If paleontology has seemed to you not to have changed conceptually overly much since your day, it has at least thrown the Darwinian blinkers off from its eyes. And it has indeed provided the gist of a novel evolutionary perspective that is only now just beginning to be tested—and in some manner accepted—by those in the biological community open to testing with their molecular data ideas suggested from the musty old bones and shells of the fossil record.

Believe me, Charles, when I echo your sentiment that nothing ill be taken on either side from this frank exchange of views. I look forward to your reply.

Sincerely,

Niles

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